1. Field of the Invention
The present invention relates generally to the field of hydraulic mechanical positioning devices such as those used for positioning the back rest of a reclining seat, and more particularly pertaining to an improved such device which allows presetting of a mechanical stop for positively limiting the length of the stroke of the positioning device.
2. State of the Prior Art
Positioning devices, in particular hydraulic positioners, have been in used for a long time and have found widespread application in recliner seats for controlling the angle of the reclining back rest to suit the preference of a seat occupant. Such hydraulic positioners are used in passenger seats on commercial airliners, where the back rest of the passenger seat is movable between a fully upright position and a more comfortable reclining position. The maximum permissible reclining angle of the back rest for a particular seat depends, among other factors, on the spacing between successive seat rows in an aircraft as well as the location of a particular seat within the aircraft. Seats adjacent to an aircraft exit, for example, may require limitation of the maximum depression of the back rest to assure adequate clearance at all times for safe passage. Seats of similar design in a particular aircraft may therefore require different limits to the recliner adjustment depending on the location on a particular seat in the aircraft. Similar considerations may apply to recliner seat installations in other vehicles, such as automotive applications.
Many recliner seat designs are known in which the angle of the reclining back rest is adjustable by means of one or more positioners such as the positioner disclosed in U.S. Pat. No. 3,860,098, issued Jan. 14, 1975 and owned by this applicant. These positioners are hydraulic devices where a rod is connected to a piston displaceable within a cylinder containing a hydraulic fluid. A valve controls fluid flow between two chambers in the cylinder. The valve is actuatable by a control typically mounted on the arm rest of the recliner seat and accessible to the seat occupant. In a normal condition of the device the valve is closed, preventing fluid flow between the two chambers and consequently locking the piston against movement relative to the cylinder. In this normal condition of the device, the rod is fixed against movement through the cylinder and the back rest is fixed in a selected position. If the occupant desires to readjust the position of the back rest, he or she actuates the valve control, opening the valve to fluid flow and permitting the rod and piston to move axially along the cylinder to a new position In the usual installation, an external coil spring of substantial size is mounted coaxially with the cylinder and compressed between the cylinder and rod, biasing the device to an extended position which usually corresponds to a fully upright position of the recliner back rest. The seat occupant repositions the back rest by first actuating the valve to an open position and then pushing backwards on the back rest to drive the rod into the cylinder against the bias of the external spring, then releasing the valve control to its normal, closed position, to lock the seat back rest at the selected new angle. The positioner is consequently adjustable through a stroke of the rod relative to the cylinder, between a fully extended and a retracted condition. In order to limit the maximum angle of depression of the recliner back rest, it is necessary to limit movement of the rod into the cylinder to stop the stroke short of the fully retracted condition otherwise possible in the particular positioner.
In the past, such limitation has called for use of customized mechanical stops in such positioners, dimensioned to meet the requirements of each particular seat installation.
A need exists for a positioning device with an integral, continuously adjustable stroke limiter, such that a stroke limit for each positioner can be easily and quickly preset at any point within a given maximum stroke of the positioner, without necessity for custom components. Such a positioner with continuously adjustable stroke limiting should be durable, dependable and of economical construction.